EP0181712B1

EP0181712B1 - Reversible underground piercing device

Info

Publication number: EP0181712B1
Application number: EP85307509A
Authority: EP
Inventors: Edward J. Bouplon
Original assignee: Allied Steel and Tractor Products Inc
Current assignee: Allied Steel and Tractor Products Inc
Priority date: 1984-10-19
Filing date: 1985-10-17
Publication date: 1988-07-27
Also published as: JPS61162696A; JPH0376398B2; CN1010421B; EP0181712A1; MX166709B; US4662457A; CN85108426A; CA1248825A; DE3564002D1

Description

This invention relates to a pneumatically operated underground piercing device and in particularto an improved mechanism for selecting the forward and reverse direction of operation of the device.
In recent years, pneumatically operated devices have been developed for creating a hole in the ground by the internal mechanism of the bullet- shaped device causing forwardly directed impacts to advance the device by compressing the soil to form the hole. The device is merely connected by a hose to a source of compressed air and aimed in the desired direction whereupon it is self-propelled through the earth to the desired destination. These devices are particularly useful in forming a generally horizontal hole under a street or other surface obstruction to install pipes, cables or the like without the necessity of digging a trench across the obstructed surface or the problems in boring a hole. A small trench is dug on either side of the surface obstruction and this pneumatically operated device is aimed from one trench to the other beneath the surface obstruction. On occasion the device will encounter an obstruction or be diverted so far off course that it is desirable or required to retractthe device and start again which requires the ability to reverse the direction of the impacts being created within the device. Also, if a vertical or other blind hole is being created by the device, it is necessary to reverse its direction of movement after reaching the desired hole depth.
Anumberof different mechanisms and methods have been developed for selectively controlling the direction of movement of these underground piercing tools but each has exhibited some undesirable characteristics for accomplishing reversing such as inconsistency, time consuming, failure, inadvertent switching, excessive maintenance, etc. The mechanisms for accomplishing reversing have taken many forms, although the basic structure performs the same function in each device of communicating the compressed air between an internal control sleeve orvalve and the reciprocating striker at two different longitudinal locations within the device to cause the striker to impact either the front end or rear end of the device depending on that longitudinal location.
For example, in U.S. Patent 3,744,576 the longitudinally movable valve sleeve is switched to the reverse operating position by reducing the pressure of the compressed air supplied to the device causing a valve element to move. In U.S. Patent 3,756,328 the valve sleeve is threadedly mounted in the device and connected to the air hose whereby its longitudinal position is changed by rotating the air hose which is a time consuming and difficult job in view of the multiplicity of revolutions required to change the longitudinal position the desired amount and the length of air hose involved.
The device of U.S. Patent 4,121,672 is in accordance with the prior art portion of claim 1. This prior device has a valve sleeve with a stepped shape at its front edge whereby only a small angular rotation, such as one quarter turn, is required for reversing but in practice it has been found that the mechanism will inadvertently reverse due to unwinding or twisting of the hose.
The devices of U.S. Patents 4,078,691 and 4,171,727 are reversible by interrupting the air pressure and pulling on the hose to reposition the valve sleeve before reapplying the air pressure, but such devices suffer from inconsistent operation or wear and failure of the components required to hold the valve sleeve in the forward or reversed positions. Numerous other devices have been designed that use one of these principles or methods for causing reversing but have similar deficiencies, such as the devices disclosed in US Patents 3 616 865, 651 874, 705 633,3 727 701, 3 763 939, 3 995 702, 4 132 277 and 4 284 147.
It is an object of this invention, which is characterised as specified in claim 1, to provide an underground piercing tool with an improved reversing mechanism operable by merely interrupting the air pressure supply and turning the air hose in one direction or the other a small but uncritical amount in either direction for causing the desired direction of movement before resupplying the compressed airwhich mechanism is not susceptible to inadvertent reversing of the direction of operation or other deficiencies of the prior art devices.
Another object of this invention is to provide an underground piercing tool wherein the valve sleeve is locked in either of two longitudinal positions for the two directions of operation by the supply of compressed air with the change of those positions being readily accomplished by interrupting the supply of compressed air and merely rotating the air hose in one direction or the other a small amount. This mechanism requires no moving parts for locking the valve sleeve in either longitudinal position.
While US-A-3 407 884 discloses a reversible underground piercing tool with a reversing valve operable to cause forward or reverse operation, depending upon its axial position, it does not have the positive simple actuation of the present invention where the controlling rotation is caused positively by rotating the hose rather than relying upon a cessation and reimposition of pressure to cause advancement of a continuous monodirectional pin and slot connection.
A preferred embodiment includes a shock absorbing mechanism for supporting the valve sleeve which does not require rubber components that tend to adversely affect the operation of the device by improper installation, inconsistent hardness, or fatigue. Preferably sound attenuating means are provided within the underground piercing tool to reduce the noise caused by the compressed air exhaust.
Other and more detailed objects and advantages of the present invention will be apparent to those skilled in the artfrom thefollowing description and the accompanying drawings, wherein:

Figure 1 is a sectional side view of a first embodiment of the underground piercing tool of this invention illustrating the valve sleeve element in the forward position for operation of this tool in the forward direction and with the striker impacting on the front of the tool for imparting forward motion.
Figure 2 is an enlarged sectional side view of the tool of Figure 1 with portions in elevation and rotated from the positions illustrated in Figure 1.
Figure 3 is a sectional side view similar to Figure 2 with the components in a position caused by interrupting the supply of compressed air.
Figure 4 is a sectional side view similar to Figures 2 and 3 but with the components in the position for causing reverse motion of the tool with the compressed air being supplied and the striker impacting the rear of the tool.
Figure 5 is a sectional side view similar to Figure 4 but illustrating thhe striker in the forward position.
Figure 6 is a sectional end view taken substantially on the line 6-6 of Figure 1.
Figure 7 is an enlarged elevation of the valve guide sleeve of the first embodiment.
FIG. 8 is a developed view of the guide slots of the valve guide sleeve of Fig. 7.
FIGS. 9 and 10 are end views of the left and right ends, respectively, of the valve guide sleeve of Fig. 7.
FIGS. 11, 12 and 13 are fragmentary sectional side views of a second embodiment of the underground piercing tool of this invention with Fig. 11 illustrating the components in the position for forward movement of the tool, Fig. 12 illustrating the components in the position upon interrupting the compressed air supply, and Fig. 13 illustrating the components in the position for reverse movement of the tool.
FIG. 14 is a side elevation view of the valve guide sleeve of the second embodiment of Figs. 11-13.
FIG. 15 is a developed view of the guide slots of the valve guide sleeve of Fig. 14.
FIG. 16 is a front (left) view of the valve guide sleeve of Fig. 14.
FIG. 17 is a fragmentary sectional elevational view of a third embodiment of the control components of the underground piercing tool of this invention.
FIG. 18 is an end elevation view of the rear support flange of the embodiment of Fig. 17.
FIG. 19 is a sectional side view of the support flange of Fig. 18 taken on the line 19-19 in Fig. 18.
FIG. 20 is a side elevation view of the valve guide sleeve of the third embodiment illustrated in Fig. 17.
FIG. 21 is a front (left) end view of the valve guide sleeve of Fig. 20.
FIG. 22 is a sectional side elevation view of the valve guide sleeve taken on the line 22-22 in Figs. 20 and 21.

Referring now to the first embodiment of this invention illustrated in Figs. 1-10 and specifically to Fig. 1, the underground piercing tool of this invention includes a hollow cylindrical body 10 having a tapered front end 11 with internal threads 12 and an open rear end 13 with internal threads 14. A pointed anvil 15 is threadedly joined to the threaded front portion 11 by the thread 12 and has a striking surface 16 at its rear end. An end cap 17 is threadedly connected to the rear end 13 of the hollow cylindrical body 10 by the threads 14 for allowing assembly and disassembly of the tool. A striker 18 is slidably mounted in the hollow body 10 to reciprocate fore and aft with a front end surface 19 for impacting on the surface 16 of anvil 15 to drive the tool forwardly. The striker 18 has an annular rear end 20 adapted to impact against the front annular end 21 of the end cap 17 for driving the tool rearwardly. The outer surface of the striker 18 near the front is provided with cylindrical portions 22 for smooth engagement with the interior cylindrical surface of the body 10 and machined flat portions 23 for allowing air to pass that portion. The rear end of the striker 18 is provided with a cylindrical portion 24 slidably engaging the interior of the hollow cylindrical body 10 and acting as a piston and cylinder arrangement. The remaining exterior portions of the striker 18 are spaced from the interior of the cylindrical body 10 to provide annular passageways for the air during operation of the device.
The striker 18 is provided with a cylindrical cavity 25 at its rear end with radial ports 26 communicating the cavity 25 with the exterior of the striker. A valve body, generally designated 30 has a cylindrical valve element 31 at its front end slidably engaging the cylindrical cavity 25 in the striker 18. Valve body 30 has a central bore 32 extending its entire length and a threaded rear end 33 to which an air hose 27 and coupling 28 are connected for supplying compressed air through the body 30 to the cavity 25 of the striker 18. As the striker 18 reciprocates within the body 10 causing the striker cavity 25 to reciprocate over the valve element 31, the ports 26 of the striker are either closed by the valve element 31 or positioned to the front or rear of the valve element 31. The longitudinal position of the valve element 31 determines whether the underground piercing tool will be operating in a forward or reversed mode by timing the opening and closing of the ports 26 to cause the striker to impact at the front surface 16 on the anvil or the rear surface 21 on the end cap.
While in the forward operating mode, when the striker 18 is in the position shown in Fig. 1, the compressed air is supplied through the ports 26 to the entire front of the striker 18 forward of the piston surface 24 urging the striker rearwardly in its return stroke. However, as the ports 26 are closed the cavity 25 and valve element 31 form a piston and cylinder which is continually supplied with compressed air and therefore tends to arrest the rearward movement of the striker 18 in opposition to the compressed air previously admitted to the front of the striker. As the ports 26 pass the rear of the valve element 31 to thereby exhaust the compressed air previously trapped in front of the striker, the compressed air within the cavity 25 drives the striker 18 forwardly to impact surface 16 to complete the cycle. By moving the valve element 31 rearwardly, as shown in Figs. 4 and 5, the compressed air is supplied through the ports 26 to the front of the striker 18 for a longer duration in the forward portion of the movement of the striker to develop a longer duration of rearward force and the ports 26 do not reach the rear end of the valve element 31 to exhaust the compressed air until immediately before the rear end 20 of the striker 18 impacts on the front end 21 of the end cap 17 thereby driving the tool rearwardly for the reverse mode of operation. This manner of operation of this reversible, pneumatic underground piercing tool, as thus far described, is the same for all three embodiments disclosed herein and is conventional as disclosed in many of the U.S. patents identified above and therefore will not be described in further detail. The present invention differs in the structure and manner for locating the valve element 31 in the two longitudinal positions for the forward and reverse modes of operation which structure and manner of operation will now be described with respect to each of the three embodiments disclosed herein.
In the embodiment of Figs. 1 through 10, the valve body 30 has a cylindrical portion 34 extending from the rear end forwardly for a substantial proportion of the valve body 30. The cylindrical portion 34 is slidably received in the cylindrical interior 35 of a valve guide sleeve, generally .designated 36, shown in detail in Figs. 7-10. The valve guide sleeve 36 is supported in the end cap 17 by an elastomeric sleeve or bushing 37 which serves as a shock absorber and support for the valve guide sleeve 36. The elastomeric bushing 37 is stretched over the vlange 38 on sleeve 36 and tightly fits the cylindrical outer surface 39 of sleeve 36. The bushing 37 in turn is press fit into the end cap 17 before assembling the end cap to the cylindrical body 10. The bushing 37 has a plurality of longitudinally extending holes 40 or other convenient shape through which the compressed air exhausts during the rearward stroke of the striker 18. A rubber valve seal 41 is also mounted on the valve guide sleeve 36 to the rear of the bushing 37 to cover the holes 40 and prevent dirt and other foreign material from entering the interior of the tool while allowing air to exhaust outwardly past the seal 41 by deflecting same.
The valve body 30 is provided with a pin 42 extending outwardly of the cylindrical surface 34 and engaging a multiposition guide slot, generally designated 43, in the valve guide sleeve 36. As thus seen in the developed view Fig. 8 (meaning the 360° circumference of the forward portion of the valve guide sleeve 36 is drawn flat) the slot 43 includes a longitudinally extending internal entrance groove 44 connected to a circumferential groove 45 for assembling the valve guide sleeve 36 and valve body 30 by the pin 42 passing in through grooves 44 and 45 of the slot 43 to the operative positions. The slot 43 includes angularly displaced depressions 46 and 47 separated by a raised portion 48 along the front edge of the slot 43 for locating the pin 42 in two separate positions 42a and 42b, respectively, shown in dashed lines in Figs. 7 and 8. The opposite or rear edge of slot 43 is provided with a deep notch or depression 49 and a longitudinal internal groove 50 extending the length of the valve guide sleeve 36. The depression 49 and groove 50 are separated by a peak 51 with inclined ramp portions 52 and 53 on either side of the peak. The depression 49 provides a third position 42c, shown in dashed lines in Figs. 7 and 8, for the pin 42 and the groove 50 allows the pin 42 to move longitudinally to a fourth position 42d, shown in dashed lines in Fig. 7 and in elevation in Figs. 4 and 5. It should be noted that the pin 42 is of a limited height to pass through the internal grooves 44 and 50 but to engage the remaining edges of the slot 43.
A coil type compression spring 54 surrounds the mid portion of valve body 30 and extends between the rear shoulder of valve element 31 and the front end 55 of the valve guide sleeve 36 to continually urge the valve body 30 forwardly relative to the valve guide sleeve 36. After the valve body 30 has been assembled to the valve guide sleeve 36 by compressing the spring 54 and manipulating the components to cause the pin 42 to pass through grooves 44 and 45 to one of the positions 42a or 42b, the air hose 27 and connector 28 may be threadedly installed on the rear end of the valve body 30 and the end cap 17 threadedly installed on the cylindrical body 10 to complete the assembly. The spacing between the connector 28 and the rear end flange 38 of the valve guide sleeve 36 is such that the pin 42 may move to any of the positions 42a-d but cannot reenter the lateral groove 45 to pass through groove 44 to allow the pin 42 to exit the slot 43 and allow the valve body 30 to become disassembled from the valve guide sleeve 36. In operation of the tool, when the supply of compressed air is interrupted, the spring 54 urges the valve body 30 forwardly whereupon the pin 42 engages the front edge of slot 43 and assumes a condition such as shown in Fig. 3 with the pin in position 42a. By rotating the hose 27 in either direction the pin 42 will move between positions 42a and 42b. Upon supplying compressed air through hose 27 to the tool, the internal pressure will urge the valve body 30 outwardly (rearwardly) causing movement of the pin 42 from position 42a to position 42c or from position 42b to position 42d. If the pin 42 is located somewhere between positions 42a and 42b, the rearward movement will cause the pin to engage one of the slopes 52 or 53 on either side of the peak 51 to slightly rotate the valve body 30 and cause the pin 42 to assume one or the other of the rearward positions 42c or 42d.
With the pin 42 located in position 42c in depression 49, the valve element 31 is properly located for opening and closing the ports 26 on the striker 18 to cause the striker to impact the front of the tool for forward motion, as previously described. With the pin 42 located in the groove 50 at the position 42d, the valve element 31 is located in its rearmost position for properly opening and closing the ports 26 to cause the striker 18 to impact on the rear end cap 17 to cause rearward movement. In either mode of operation, the striker 18 does not impact against the opposite end but rather is arrested by compressed air. In other words, in the forward mode of operation the compressed air in cavity 25 produces a magnitude of force to slow the striker 18 and reverse its motion before the rear end 20 impacts against the end cap 17. Similarly, in the reverse mode of operation, the air trapped inside the cylindrical hollow body 10 in front of the striker 18 by closing of the ports 26 during forward motion of the striker slows the striker to a stop and reverses its motion without the front end 19 impacting on the surface 16 of anvil 15. Thus, all of the impacts are imposed in the proper direction for causing the desired movement of the tool depending on the position of the valve body 30.
With the aforedescribed structural arrangement, it may be seen that the direction of movement of the tool may be changed by merely interrupting the supply of compressed air and rotating the hose 27 approximately a quarter of a turn in the clockwise direction (as viewed from the rear of the tool) to position 42a of the pin for the forward mode of operation and a quarter of a turn in the counterclockwise direction to position 42b for the reverse mode of operation. Resumption of the supply of compressed air automatically moves the valve body 30 longitudinally to the proper position 42c or 42d as controlled by the pin 42 in slot 43.
Referring now to the second embodiment of the invention shown in Figs. 11 through 16, many of the components are identical and will be so identified by the identical numeral without detailed description while other elements are similar and will be given the same numerals in the 100 series. Again, the striker 18 is slidably mounted in the hollow cylindrical body 10 to which is connected the end cap 17 supporting the elastomeric shock absorber bushing 37 which in turn supports a modified form of valve guide sleeve 136 in the rear of the underground piercing tool. The valve guide sleeve 136 has an elongated forward portion containing the entire multiposition guide slot, generally designated 143, which includes an entrance opening 144 for receiving the pin 142 during assembly of the valve body 130 to the valve guide sleeve 136. Further, the slot 143 includes a depression 146 for defining a forward position 142a for the pin and a deep notch or depression 149 longitudinally spaced therefrom for defining a second position 142c for the pin. A longitudinal groove 150 provides a third position 142d for the pin and again there are sloped portions 152 and 153 on either side of the peak 151 for causing the pin 142 to assume the position 142c or 142d upon the introduction of compressed air to the tool in a manner identical to that described with respect to the first embodiment. The remaining position 142b, shown in dashed lines in Fig. 15, for the pin is in an open portion of the slot 143 but the valve body 130 is prevented from moving further forward relative to the valve guide sleeve by a snap ring 160 on the rear end of the valve body 130 engaging the rear flange 138 on the valve guide sleeve 136. In this embodiment, the pin 142 may be substantially longer than in the first embodiment since it need not pass into a shallow longitudinal such as groove 50 in the valve guide sleeve 36. This provides greater resistance to wear of the pin 142 and slot 143. The operation of this second embodiment is identical to that of the first embodiment.
Referring now to the third embodiment of this invention shown in Figs. 17 through 22, the components are installed in the end cap 17 which is then assembled to the hollow cylindrical body 10 (not shown) with striker 18 (not shown) and similar components will be described using numerals in the 200 series. Here the elastomeric shock absorbing bushing 37 is eliminated but a valve seal 41 (not shown) may be used if desired. The valve guide sleeve 236 has a radial flange portion 270 with an external diameter slightly smaller than the internal diameter of end cap 17 to allow some movement and misalignment. A support flange 271 has a collar portion 272 and an internal bore 273 for slidably receiving the external cylindrical surface 274 of the valve guide sleeve 236. A coil type compression spring 275 extends between the flanges 270 and 271 to perform a shock absorbing function. The flange portion 270 of valve guide sleeve 236 is held in position by a snap ring 276 and the rear support flange 271 has a spherical surface 277 for engaging a similar internal spherical surface 278 on the end cap 17. The spring 275 is preloaded by an amount approximately equal to the reactive load created by the compressed air supply when the tool is in operation whereby, in effect, the forward force by the flange 270 on snap ring 276 by the spring 275 is reduced to approximately zero and therefore the assemblage of valve guide sleeve 36, support flange 271 and spring 275 somewhat "float" within end cap 17 during operation to allow for misalignment and to absorb the shocks caused by the impacting at each end.
This third embodiment incorporates a sound attenuating feature by providing the flanges 270 and 271 with a multiplicity of tapered holes 240 through which the escaping air passes. The holes 240 in flange 270 are misaligned with the holes 240 in flange 271 to inhibit the direct transmission of sound. Further, the holes 240 in flange 270 are taped in the direction to cause contraction of the air while the holes 240 in flange 271 are taped in the opposite direction to allow expansion of the air thereby attenuating the sound caused by the exhaust air.
Again, with this third embodiment as with the preceding embodiments, the valve guide sleeve 236 is provided with a multiposition slot, generally designated 243, that is engaged by a pin 242 on the valve body 230 for defining the position of the valve body 230 relative to the valve guide sleeve 236 and the balance of the tool. A deep notch or depression 249 defines the position for the pin in the forward operating mode of the tool and the longitudinal groove 255 defines the position for the pin in the reverse mode of operation. The pin 242 is confined to the slot 243 after assembly by the hose connector 28 adapted to engage the rear end 279 of the valve guide sleeve 236. Again, the manipulation required to cause reversing of the direction of movement of this third embodiment is the same as the two preceding embodiments, namely, merely interrupting the air pressure and rotating the air hose 27 in one direction or the other before resupplying compressed air.

Claims

1. A reversible pneumatic underground piercing tool having an outer housing (10) having mounted therein an elongated tubular valve member (30) having one end provided with means (28) for connection to a pneumatic hose (27) for the supply of compressed air and for rotating the valve member relative to said housing when pneumatic pressure is disconnected therefrom, said valve member (31) being received within a chamber (25) in a hammer piston (18) reciprocable in said housing and cooperating with an aperture (26) through the side of the piston chamber whereby the supply of compressed air to the valve member will cause reciprocation of the hammer piston in said housing, said valve member in different selected rotated positions (42c, 42d) being so located as to actuate the hammer piston to cause forward or backward movement of the tool as required, characterised in that the valve member is axially locatable in two axially displaced positions (42c, 42d) respectively to control forward and reverse movement of the tool, there being provided interengaging means (142, 143) for guiding and restricting movement of the valve member (131) relative to the housing whereby when the pneumatic pressure is disconnected the valve member is rotatable in one axial position by rotation of the hose between two different predetermined angular positions (42a, 42b) less than 360° apart, said interengaging means including means (49, 50) for guiding the valve member to one or other of said two axially displaced positions (42c, 42d) upon reconnection of pneumatic pressure depending upon the particular one of the two angular positions (42a, 42b) occupied.

2. A tool according to claim 1, characterised in that a sleeve (36) movably supports the valve member relative to the housing, and said interengaging means comprises a pin and slot means between the sleeve and the valve member.

3. A tool according to claim 2, characterised in that said pin and slot means comprises a pin (42) on the exterior of said valve member and a slot (43) in said sleeve.

4. A tool according to claim 3, characterised in that said slot includes a depression (46, 48) in an edge facing toward said one end at the angular position for forward mode operation of the tool for positioning the pin therein upon interrupting the compressed air supply.

-5. A tool according to claim 3 or 4, characterised in that said slot includes an entrance groove (44) for assembling the valve member and sleeve and two longitudinally spaced depressions (46, 49 and 47, 50) at each angular position for receiving and positioning the said pin (42) upon supplying or interrupting compressed air to said valve member in either of the two different angular positions.

6. A tool according to claim 5, characterised in that said slot includes longitudinally and circumferentially inclined surfaces (52, 53) between the two angular positions of the pin for causing the pin to enter one or the other of said depressions.

7. A tool according to claim 3 or 4, characterised in that the slot (143) is located on a radially unobstructed wall portion of said sleeve and the pin (142) extends entirely through that wall portion.

8. A tool according to claim 3 or 4, characterised in that the slot (143) is located on an end portion of said sleeve away from said one end and is open on that end, and abutment means (160) are provided on an extending end portion of said valve member and sleeve means toward said one end for limiting the longitudinal movement of . said valve member relative to said sleeve in a direction away from said one end by biasing means (54) to prevent the pin from becoming disengaged from said slot.

9. A tool according to any one of claims 3 to 8, characterised in that the slot includes an edge facing away from said one end with longitudinally and circumferentially inclined portions (52, 53) for causing the pin to be positioned in one or the other of the two axially spaced positions by causing angular relative movement upon supplying compressed air unless the pin is already aligned in one of the two angular positions.

10. A tool according to any one of claims 2 to 9, characterised in that said sleeve has a radially extending flange (270) at one end and a flanged support collar (271) slidable thereon at the other end with a compression spring (275) therebetween for supporting said sleeve in shock absorbing relation in the tool.

11. A tool according to claim 10, characterised in that the compression spring is a metal coil-type compression spring (275).

12. A tool according to claim 10 or 11, characterised in that said support collar (271) is on the outer end of said sleeve and has spherical seal engagement with the tool for accommodating mis-alignment and movement.

13. A tool according to claim 10, 11 or 12, characterised in that said flange and flange support each have longitudinally extending holes (24) therethrough for the exhausting of compressed air.

14. A tool according to claim 13, characterised in that said holes are circumferentially misaligned between the two flanges.

15. A tool according to claim 13, characterised in that said holes are tapered.

16. A tool according to claim 15, characterised in that the holes in the innermost flange have a converging taper and the holes in the outermost- flange have a diverging taper in the direction of exhausting air flow.

17. A tool according to any preceding claim, characterised in that the two predetermined angular positions are displaced by substantially 90°.

18. A tool according to any preceding claim, characterised in that a biasing means (54) urges the valve member toward the front end in opposition to the compressed air forces whereby upon interruption of the compressed air supply the valve member will be moved longitudinally to a position for allowing shifting of the valve member to one of the two axially displaced positions upon renewed supply of compressed air.

19. A tool according to claim 1, characterised in that the valve member is supported in the housing by supporting means which includes taper holes for the passage of exhausted air, said holes being arranged to attenuate the sound of the exhausting air.